Evolution

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Evolution
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What is a theory?

• A widely accepted explanatory idea that is broad
  in scope and supported by a large body of
  evidence.
• http//www.pbs.org/wgbh/evolution/library/11/2/e_s
  _1.html

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What is evolution?

• History of defining evolution
• About 2,500 years ago, the Greek philosopher
  Anaximander
• promoted the idea that life arose in water and
  that simpler forms of life preceded more complex
  ones.
• The Greek philosopher Aristotle
• generally held that species are fixed, or
  permanent, and do not evolve.
• Judeo-Christian culture
• fortified this idea with a literal interpretation
  of the Book of Genesis, holding that all species
  were individually designed by a divine creator.
• The idea that all living species are static in
  form and inhabit an Earth that is most about
  6,000 years old dominated the intellectual and
  cultural climate of the Western world for
  centuries.

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What is evolution?

• History of defining evolution
• Carl Linneaus (18th century)
• The father of taxonomy.
• Used binomial nomenclature, came up with the
  hierarchical classification theme, used visible
  characteristics to classify plants and animals.
• Thomas Malthus (18th 19th century)
• Attempedto justify the conditions of the poor by
  stating that poverty and starvation were merely a
  consequence of overpopulation.

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What is evolution?

• History of defining evolution
• Lamarck (18th 19th century)
• First to publish a reasoned theory of evolution
  A) the idea of use and disuse B) inheritance of
  acquired characteristics
• Lyell (19th century)
• natural processes form geological formations over
  a long period of time, erosion and other forces
  that shape rocks are very slow processes that
  take millions of years, so the earth must be
  older than previously believed.
• Wallas (19th 20th century)
• theory of evolution by natural selection.

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What is evolution?

• History of evolution (continued)
• In the early 1800s, French naturalist Jean
  Baptiste Lamarck suggested that the best
  explanation for this relationship of fossils to
  current organisms is that life evolves.
• Today, we remember Lamarck mainly for his
  erroneous view of how species evolve.
• He proposed that by using or not using its body
  parts, an individual may develop certain traits
  that it passes on to its offspring.
• Larmarcks idea is known as the inheritance of
  acquired characteristics.
• He suggested, for instance, that the ancestors of
  the giraffe had lengthened their necks by
  stretching higher and higher into the trees to
  reach leaves.
• Although his ideas were incorrect, he helped to
  set the stage for Darwin by strongly advocating
  evolution and by proposing that species evolve as
  a result of interactions with their environment.

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What is evolution?
Charles Darwin
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What is evolution?

• Charles Darwin
• Born in 1809, the same year that Lamarck
  published some of his ideas on evolution.
• In December 1831, at the age of 22, Darwin began
  a round-the-world sea voyage that profoundly
  influenced his thinking and eventually the
  thinking of the entire world.
• He accompanied the captain of the HMS Beagle, a
  surveying ship, on a mission to chart poorly
  known stretches of the South American coastline.
• Darwin actually spent most of his time onshore,
  collecting thousands of specimens of fossils and
  living plants and animals.
• He noted the unique adaptations of these South
  American organisms in places as different as the
  Brazilian jungle, the grasslands of the pampas,
  and the frigid Anarctica.
• He asked himself why fossils of the South
  American continent were more similar to modern
  South American species than to fossils of other
  continents.

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What is evolution?

• Charles Darwin (continued)
• Other questions arose from Darwins visit to the
  Galapagos Islands.
• Darwin observed that these islands had many
  unique organisms, most of which were similar to,
  but different from, the plants and animals of the
  nearest mainland.
• Even the individual islands had some species that
  differed from those on other islands.
• Referring to the islands and their unique
  inhabitants, he later wrote, Both in space and
  time, we seem to be brought somewhat near to that
  great factthat mystery of mysteriesthe first
  appearance of new beings on the earth.

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What is evolution?

• Charles Darwin (continued)
• While on the voyage, Darwin read and was strongly
  influenced by the recently published Principles
  of Geology, by Scottish geologist Charles Lyell.
• Lyells work led Darwin to realize that natural
  forces gradually change Earths surface and that
  these forces are still operating in modern times.
• Darwin had collected fossils of marine snails in
  the Andes. Having read Lyells book and witnessed
  an earthquake that raised part of the coastline
  of Chile almost a meter, he came to believe that
  slow, natural processes such as the growth of
  mountains as a result of earthquakes, could
  account for the presence of marine snails on
  mountaintops.

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What is evolution?

• Charles Darwin (continued)
• Upon Darwins return to Great Britain after his
  voyage, his experiences and reading had led him
  to doubt seriously that Earth and living
  organisms were unchangeable and had been
  specially created only a few thousand years
  earlier.
• He analyzed his collections, discussed them with
  colleagues, continued to read, and maintained
  extensive journals of his observations, studies,
  and thoughts.
• By the early 1840s, he had composed a long essay
  describing the major features of his theory of
  evolution. He realized that his ideas would cause
  a social furor, however, and he delayed
  publishing his essay.
• In the mid 1850s, Wallace conceived a theory
  almost identical to Darwins. He asked Darwin to
  evaluate the manuscript he had written about his
  theory to see if it merited publication.
• In 1858, two of Darwins colleagues presented
  Wallaces paper and excerpts of Darwins earlier
  essay together to the scientific community.

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What is evolution?

• Charles Darwin (continued)
• He published his book On the Origin of Species by
  Means of Natural Selection in 1859.
• He presented the world with an avalanche of
  evidence and a strong, logical argument for
  evolution. He also described his theory of
  natural selection, an explanation of how
  evolution occurs.
• In the first edition of his book, Darwin did not
  actually use the word evolved until the very end,
  referring instead to descent with modification.
• This phrase summarized Darwins view of life he
  perceived a unity among species, with all
  organism related through descent from an ancestor
  that lived in the remote past.
• As the descendants of that ancestor spread into
  various habitats over millions of years, they
  accumulated diverse modifications, or
  adaptations, that accommodated them to diverse
  ways of life.
• The history of life seemed to resemble a tree,
  with multiple branchings from a common trunk to
  the tips of the twigs.
• At each fork of the evolutionary tree is an
  ancestor common to all lines of descent branching
  from that fork.
• Species that are closely related share many
  characteristics because their lineage of common
  descent extends to the smallest branches of the
  tree of life.

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Natural Selection

• Darwins Theory of Evolution is based on several
  key observations and inferences
• 1. Overproduction of offspring
• Populations produce too many offspring, many must
  die.
• 2. Struggle for existence
• Food, water, and other resources are limited
  organisms compete with one another for these
  resources
• 3. Variation
• Individuals exhibit variation in a population and
  have a unique set of traits, and these traits get
  passed on from one generation to the next.
• Some of these traits will improve their chance
  for survival while others are less favorable.
• 4. Differential reproduction
• Within a varied population, individuals whose
  characteristics adapt them best to their
  environment are most likely to survive and
  reproduce these individuals thus tend to leave
  more offspring than less fit individuals do.
• Reproduction is central to what Darwin saw as the
  basic mechanism of evolution, the process he
  called natural selection.
• Means by which the environment filters
  variations, favoring some over others.
• Allows for a gradual change in characteristics of
  a population of organisms overtime

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Artificial Selection

• Darwin found convincing evidence for his ideas in
  the results of artificial selection, the
  selective breeding of domesticated plants and
  animals.
• He saw that by selecting individuals with the
  desired traits as breeding stock, humans were
  playing the role of the environment and bringing
  about differential reproduction.
• They were, in fact, modifying species.
• Darwin reasoned that if so much change could be
  achieved in a relatively short period of time by
  artificial selection, then over hundreds or
  thousands of generations natural selection should
  be able to modify species considerably.
• Such changes could account for the evolution of
  new species.

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Evidence of Evolution

• Darwin developed his theory of descent with
  modification mainly with evidence from the
  geographic distribution of species, examples of
  artificial selection, and the fossil record.
• His careful documentation convinced many of the
  scientists of his day that organisms do indeed
  evolve.
• 1. Fossil record
• 2. Biogeography
• 3. Comparative anatomy
• 4. Comparative embryology
• 5. Molecular biology

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Evidence of Evolution

• 1. Fossil record
• Fossils document some of the drastic changes that
  life has undergone over time.
• The organic substances of a dead organism usually
  decay rapidly, but hard parts of an animal that
  are rich in minerals, such as the bones and teeth
  of dinosaurs and the shells of clams and snails,
  may remain as fossils.
• The fossil recordthe ordered array in which
  fossils appear within layers of sedimentary
  rockprovides some of the strongest evidence of
  evolution.
• Sedimentary rocks form from layers (strata) of
  sand and mud that settle to the bottom of seas,
  lakes, and marshes.
• Younger strata are on top of older ones thus,
  the relative ages of fossils can be determined by
  the layers in which they are found.
• Fossil record shows that the oldest known
  fossils, dating from 3.5 billion years ago, are
  prokaryotes.
• Fossils in younger layers reveal the evolution of
  various groups of eukaryotic organisms.

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Evidence of Evolution
http//www.pbs.org/wgbh/evolution/library/03/3/l_0
33_01.html
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Evidence of Evolution

• 2. Biogeography
• It was the geographic distributing of species,
  known as biogeography, that first suggested to
  Darwin that organisms evolve from common
  ancestors.
• Darwin noted that Galapagos animals resembled
  species of the South American mainland more than
  they resembled animals on similar but distant
  islands.
• The logical explanation was that the Galapagos
  species evolved from South American immigrants.
• http//www.ucmp.berkeley.edu/geology/anim1.html

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Evidence of Evolution

• 3. Comparative Anatomy
• The comparison of body structures in different
  species.
• Anatomical similarities between many species give
  signs of common descent.
• Similarity in characteristics that results from
  common ancestry is known as homology.
• Homologous structures are features that often
  have different functions but are structurally
  similar because of common ancestry.
• For example, the same skeletal elements make up
  the forelimbs of humans, cats, whales, and bats,
  all of which are mammals. However, the functions
  of these forelimbs differ.
• The logical explanation is that the arms,
  forelegs, flippers, and wings of different
  mammals are variations on a common anatomical
  plan that has become adapted to different
  functions.

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Evidence of Evolution
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Evidence of Evolution

• 3. Comparative Anatomy (continued)
• Some of the most interesting homologous
  structures are vestigial organs, structures of
  marginal, if any, importance to the organism.
• Remnants of structures that served important
  functions in the organisms ancestors.
• For example, the small hind-leg and foot bones of
  modern whales, the skeletons of some snakes
  retain vestiges of the pelvis and leg bones of
  walking ancestors.

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Evidence of Evolution

• 4. Comparative Embryology
• The comparison of early stages of development,
  called comparative embryology, is another major
  source of evidence fro the common descent of
  organisms.
• One sign that vertebrates evolved from a common
  ancestor is that all of them have structures on
  the sides of the throat called pharyngeal
  (throat) pouches.
• At this stage, the embryos of fishes, frogs,
  snakes, birds, and mammals look relatively alike.
• They take on more and more distinctive features
  as development progresses.
• For example, pharyngeal pouches develop into
  gills in fishes, but into parts of the ears and
  throats in humans.

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Evidence of Evolution
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Evidence of Evolution

• 5. Molecular Biology
• Recent advances in molecular biology have enabled
  biologists to read a molecular history of
  evolution in the DNA sequences of organisms.
• If two species have genes with sequences that
  match closely, biologists conclude that these
  sequences must have been inherited from a
  relatively recent common ancestor.
• In contrast, the greater the number of sequence
  differences between species, the less likely they
  share a close common ancestor.
• Molecular comparisons between diverse organisms
  have allowed biologists to develop hypotheses
  about the evolutionary divergence of major
  branches on the tree of life.
• Studies of the amino acid sequences of similar
  (homologous) proteins in different species have
  been a rich source of data about evolutionary
  relationships.
• By comparing the amino acid sequence of
  hemoglobin, the following hypothesis was made
  about evolutionary relationships Rhesus monkeys
  are much more closely related to humans that are
  lampreys mice, chickens, and frogs fall in
  between.
• This hypothesis agrees with conclusions from
  comparative anatomy and embryology, along with
  fossil evidence.

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Evidence of Evolution

• 5. Molecular Biology (continued)
• There is also evidence showing that most (if not
  all) multicellular eukaryotes have similar genes
  regulating their early development.
• The logical explanation is that these genes first
  arose in a common ancestor.
• Darwins boldest hypothesis is that all
  life-forms are related.
• Molecular biology has provided strong evidence
  for it All forms of life use DNA and RNA, and
  the genetic code is essentially universal.
• This genetic language has been passed along
  through all the branches of evolution ever since
  its beginnings in an early form of life.
• http//www.pbs.org/wgbh/evolution/library/03/4/l_0
  34_04.html

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Natural Selection in Action

• Many cases of natural selection in nature have
  been documented.
• A classic example involves finches in the
  Galapagos Islands over a period of 20 years.
• The research of scientists showed measurable
  changes in in beak size in a population of ground
  finches.
• In dry years, when small seed are in short
  supply, birds must eat more large seeds. Birds
  with larger, stronger beaks have a feeding
  advantage and greater reproductive success, and
  the average beak depth for the population
  increases.
• During wet years, smaller beaks are more
  efficient for eating the now abundant small
  seeds, and the average beak depth decreases.

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Natural Selection in Action
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Natural Selection in Action

• Evolution in pesticide resistance in hundreds of
  insect species.
• Pesticides are poisons used to kill insect pests
  in farmlands, swamps, backyards, and homes.
• Whenever a new type of pesticide is used to
  control agricultural pests, a relatively small
  amount of poison dusted onto a crop may kill 99
  of the insects, but subsequent sprayings are less
  and less effective.
• The few survivors of the first pesticide wave are
  insects with genes that somehow enabled them to
  resist chemical attack. So, the poison kills most
  members of the population, leaving the resistant
  individuals to reproduce and pass the genes for
  pesticide resistance to their offspring.
• The proportion of pesticide-resistant individuals
  increases in each generation.
• Like the finches, the insect population has
  adapted to environmental change through natural
  selection.

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Natural Selection in Action

• Antibiotics Resistance
• Antibiotics are drugs that disable or kill
  infectious microorganisms.
• Most antibiotics are naturally occurring
  chemicals derived from other microorganisms.
• Pencillin, for example, was originally isolated
  from a mold and has been widely prescribed since
  the 1940s. A revolution in human healthy rapidly
  followed its introduction, rendering many
  previously fatal diseases easily curable (such as
  strep throat and surgical infections).
• During the 1950s, some doctors even predicted the
  end of human infectious disease. Unfortunately,
  evolution destroys the optimism of this
  prediction.
• In the same way that pesticides select for
  resistant insects, antibiotics select for
  resistant bacteria.
• The genes that confer such antibiotic resistance
  are often carried on R plasmids, which are passed
  on to bacterial offspring and may even be
  transferred to other bacteria.
• For nearly every antibiotic that has been
  developed, a resistant strain of bacterium has
  appeared within a few decades.
• For example, some strains of the
  tuberculosis-causing bacterium are now resistant
  to all three of the antibiotics commonly used to
  treat the disease.

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Natural Selection in Action

• Antibiotics Resistance (continued)
• In some ways, we are contributing to the problem
  of antibiotic resistance
• Livestock producers add antibiotics to animal
  feed as a growth promoter.
• As a result, much of the packaged meat for sale
  in supermarkets contains bacteria that are
  resistant to standard antibiotics.
• Doctors contribute to the problem by
  overprescribing antibiotics, for example, to
  patients with viral infections, which do not
  respond to antibiotic treatment.
• And patients contribute to this problem through
  misuse of prescribed antibioticsfor example, by
  prematurely stopping the medication before they
  feel better. This allows mutant bacteria that may
  be killed more slowly by the drug to survive and
  multiply. Subsequent mutations in such bacteria
  may lead to full-blown antibiotic resitance.
• During the anthrax crisis of 2001, public health
  officials urged panicked citizens to avoid
  unnecessarily taking ciprofloxacin (Cipro), the
  drug used to treat the deadliest form of anthrax,
  because doing so could select for resistant
  bacteria.

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Genetic Variation- Where does it come from?

• Individual variation occurs in populations of all
  species that reproduce sexually.
• Fresh assortments of existing alleles arise every
  generation from three random components of sexual
  recombination crossing over, independent
  assortment of homologous chromosomes, and random
  fertilization.
• Mutation is the ultimate source of the genetic
  variation that serves as raw material for
  evolution.
• Mutations are changes in the nucleotide sequence
  of DNA that can create new alleles.
• Most mutations occur in body cells and are lost
  when the individual dies.
• Only mutations in cells that produce gametes can
  be passed to offspring and potentially affect a
  populations gene pool.

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How Does Evolution Work?

• Populations (group of organisms that belong to
  the same species) change over time and evolve,
  not individual organisms (unlike Lamarcks idea)
• Mutations (small changes in the nucleotide
  sequence of DNA) result in new traits and
  increasing variation in the population
• One mutation alone usually does not change the
  population, however, beneficial mutations can
  change the population

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How Does Evolution Work?

• Genetic drift change in the allele frequency in
  a population based on chance
• Founder effect small group of organisms move
  away from the main population and give rise to a
  new population
• Bottleneck effect after a natural disaster, a
  small group of organisms with different
  characteristics survive

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How Does Evolution Work?

• Gene flow
• movement of organisms from one population to
  another
• Natural selection (this is already familiar)
• Nonrandom mating coolness
• For example males with the largest or most
  colorful adornments are often most attractive to
  females.
• May pose some risks? male birds with flashy
  colors may be more visible to predators but
  every time a female chooses a mate based on
  certain appearance or behavior, she perpetuates
  the alleles that caused her to make that choice
  and allows a male with a particular phenotype to
  perpetuate his alleles.

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How Does Evolution Work?
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Modern Evolutionary Theory

• Several scientists improved on Darwins theory
  and this improvement is still going on.
• Today we explain the reasons for evolution with
  mutations, changes in DNA and sexual
  reproduction.
• Evolution is closely related to genetics.
• Genetic change in a population or species over
  generations all the changes that transform life
  on Earth the heritable changes that have
  produced Earths diversity of organisms.